UNGULATA. 425 



turn (" cloison "), and the incisor teeth are wanting in the adult 

 (. tichorhinus). 



2. Those in which there is no bony partition between the 

 nostrils, and the incisors are of medium size (Rhinoceros mega- 

 rhinus]. 



3. Those in which there is no " cloison," and the incisors 

 are of large size (Rhinoceros incisivus). 



4. Those in which there is an imperfect bony partition be- 

 tween the nostrils (Rhinoceros Etruscus and R. hemitcechus'). 



The most important extinct forms of the genus Rhinoceros 

 are the R. tichorhinus, R. megarhinus, R. hemitcechus ( R. 

 leptorhinus, Owen), R. Etruscus, and the hornless species con- 

 stituting the sub-genus Acerotherium. 



The Rhinoceros tichorhinus is generally known as the 

 " Woolly Rhinoceros," from its possession of a woolly cover- 

 ing. Its skin was foldless, and it possessed two horns, of 

 which the anterior one was very large. The limbs are ex- 

 tremely stout, and the nostrils are completely separated by an 

 osseous septum. R. tichorhinus is essentially a northern form, 

 and has the same distribution in space as the Mammoth, except 

 that it did not cross Behring Straits, and is therefore not 

 found in America. In time, it is younger than the Mammoth, 

 not being found in the prae-glacial forest-bed of Norfolk, and 

 occurring for the first time in the Lower Brick-earths of the 

 Thames valley (proe-glacial, but younger than the "forest- 

 bed"). It is, therefore, essentially a Post-glacial Mammal, 

 and it is mainly found in quaternary cave-deposits and valley- 

 gravels. A molar tooth of this well-known form is figured 

 below (fig. 351). 



Fig. 350. Penultimate molar of the Fig. 351. Penultimate molar of the 

 lower jaw of Rhinoceros megarhinus, lower jaw of Rhinoceros tichorhinus, 

 two-thirds of the natural size. Post- two-thirds of the natural size. Post- 

 Pliocene. Pliocene. 



The Rhinoceros hemitcechus of Falconer ( = the R. leptorhinus 

 of Owen) is also provided with two horns, but is of a much 



